For bigger riders 20 might be a bit too small to be effective - but man, it would be loose. I&#39;ve tried down to 21 but for typical PA80 prefer 22-23 in Drake Natural - and 23 that should be good for up 5.0 without too much problem. 25 could also be a goer, but generally I would be considering that for trying to make the 80 go (with big guys) in the 5.5m+ range which again is doable but a bit after the "sweetspot" range.(and more into crossover as you said c/w real wave tuning).

Also noting the usual variances between fin "performance size" to "mechanical" (measured) or "stated" (whatever they write on it) size/s, generally with the Drake Natural Waves you can tend to use a cm size larger c/w more "typical" wave fins etc , which is to say a 23 Natural is like a 22 classic etc.